<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var str ="hello world";
        //非空字符进行布尔判断时会被理解为布尔值 ture
        if(str){
            alert("值为真")
        }
    </script>
</body>
</html>